1. Field of the Invention
The invention relates to an articulated milling arm for a dental milling instrument, the middle portion of the milling arm being connected in a horizontally swivelling manner to a first vertical articular axle which is fixed with respect to the frame, and to a second vertical articular axle which is rigidly connected to a support for a milling unit, with a common clamping device acting on both articular axles for the purpose of fixing the articulated milling arm.
2. Description of the Related Art
When dental objects such as dental casts and prosthodontic parts are milled, certain milling processes can only be carried out with a milling unit that is mobile in the horizontal plane, due to the anatomical tooth shapes which are to be milled. A horizontally mobile articulated milling arm is therefore required for this purpose, the support for which conventionally comprises a linear unit which enables a movement of the milling unit perpendicular to the plane of movement of the articulated milling arm. Known articulated milling arms for such dental milling instruments typically consist of several articulated arm members connected by articulations, which enable the requisite mobility in the horizontal plane.
For other processing operations typically carried out with such dental milling instruments, for example drilling or thread cutting, it is necessary to construct the articulated milling arm to be rigid and, particularly in the horizontal plane, immovable, whereby only the linear unit which is fitted to the articulated milling arm is permitted to exhibit a degree of freedom in the direction of the processing axis. Because such drilling and cutting operations have to be performed with a high degree of precision, the articulated milling arm which is rigid during processing has to exhibit a high degree of stiffness and inflexibility.
In order to satisfy these contradictory requirements, dental milling instruments have been developed which comprise two different milling arms: one milling arm being of articulated construction and exhibiting the required horizontal mobility, whereas a second milling arm is of rigid construction and exhibits the requisite stiffness and inflexibility for the intended drilling and cutting operations. The efforts required for such constructions are considerable.
Other known milling instruments resolve these requirements by providing articulations of the articulated milling arm which are capable of being fixed by clamping devices. As a result, a second, rigid milling arm can be dispensed with. In the case of a known dental milling instrument (DE 36 11 518 C2), a mechanical fixation of the articulations is accomplished by means of mechanical clamping devices which have to be actuated separately, for example by means of toggles or handwheels. In this case, the construction of several grips is required in order to fix the articulated milling arm. In addition, the locking action depends on the manual forces applied in each instance by the user.
It is also known to provide a separate electromagnetic braking device for each articulation of an articulated milling arm for a dental milling instrument. Although it is possible to remotely control the device by this means, the efforts in constructing such a device are considerable. Also, due to the type of construction, the clamping forces which can be achieved are relatively small, so that in the case of greater loads, a yielding of the lock results in imprecise operations. This disadvantage also exists in the case of a mechanical lock, if the clamping forces to be applied by the user are undefined or are too small, so that in this instance also there is a risk of imprecise operations.
In the case of a known articulated milling arm of the type specified at the outset (DEG 94 16 767.2 U1), the common clamping device acting on the two articular axes is actuated by means of a wing nut that has to be tightened by hand. Also in this case, the clamping forces achieved depend on the manual force applied in each instance by the user; the sequence of movements for which is not ergonomic. Further, this configuration does not allow remote control.
It is therefore an object of the invention to design an articulated milling arm in such a way that with a relatively simple structural configuration, high clamping forces can be applied to the articulations of the articulated milling arm by remote control, so that a reliable and ergonomically advantageous sequence of operations is made possible.
The invention provides an articulated milling arm designed in such a way that with a relatively simple structural configuration, high clamping forces can be applied to the articulations of the articulated milling arm by remote control, so that a reliable and ergonomically advantageous sequence of operations is possible. The invention provides two articular axles, each comprising a braking surface, and an axially mobile braking plate capable of being pressed against both braking surfaces by means of a common brake-actuating device which is actuated by pressure means.
The actuation of the common braking plate by pressure means enables the application of high braking forces to both articulations, so that a reliable fixation of the articulated milling arm is ensured. The remote control of the brake-actuating device enables a simple and ergonomic sequence of operations, whereby the high clamping forces that are applied do not depend on the manual force of the user.
The braking plate is preferably connected to a pneumatically or hydraulically pressurizable diaphragm having a large area. The use of a diaphragm as a driving member which is actuated by pressure means enables a relatively simple type of construction with large surfaces which are pressurized by pressure means, so that high clamping forces can be generated with relatively low pressure.
The diaphragm preferably bears against the braking plate. A pressure chamber, located on the opposite side of the diaphragm, is preferably capable of being pressurized pneumatically or hydraulically. This results in a particularly simple transmission of the pneumatically- or hydraulically-generated forces to the braking plate.
It is particularly advantageous if the pressure chamber extends substantially over the entire area of the braking plate. By this arrangement, the entire available area of the braking plate is pressurized.
Further advantageous configurations of the inventive concept are described in the claims of the application. Additional variations and modifications will be apparent to those skilled in the art.